1. Field of the Invention
The present invention relates to a sheet processing apparatus, an image forming apparatus, and an image forming system that deforms a spine of a booklet made of a folded sheet bundle.
2. Description of the Related Art
Conventionally, when a sheet bundle including about 20 or more sheets is folded at a time, a booklet is formed having a vicinity of a spine being curved. The folded state of the booklet including the sheet bundle folded as described above is insufficient, so that the booklet is soon opened even after it is folded. Therefore, the appearance is degraded. The booklet described above cannot lie flat, so that it is difficult to stack a great number of booklets.
In order to solve the problem described above, there has been proposed a method and an apparatus of squaring a spine of a booklet as one of deforming processes in which the spine of the booklet is pressed to be deformed into a rectangular shape (U.S. Pat. No. 6,692,208).
According to a conventional apparatus illustrated in FIGS. 21A to 21F, a booklet 701 is conveyed by conveying portions 706 and 707 with a spine of the booklet 701 set to the leading position, and the spine of the booklet 701 is brought into contact with a positioning portion 705 for positioning (FIG. 21B). Then, as illustrated in FIG. 21C, grip portions 702 and 703 nip the adjacent portion of the spine of the booklet 701, and the positioning portion 705 is retracted. A pressing roller 704 travels along the spine of the booklet 701, which projects from the grip portions 702 and 703 and which is curved, so as to apply pressure. In this manner, the curved spine of the booklet 701 is deformed into a rectangular shape.
FIG. 21A is a schematic diagram illustrating the traveling direction of the pressing roller 704. The pressing roller 704 is retracted to an area where it is not in contact with the booklet 701, before the grip portions 702 and 703 nip the booklet 701. When the grip portions 702 and 703 nip and hold the booklet 701, the pressing roller 704 moves from one end to the other end of the booklet 701 as applying pressure to the spine.
FIG. 21E illustrates the spine, which is pressed and squared, of the booklet 701, while FIG. 21D illustrates the state in which the booklet 701, which has already been subject to the deforming (squaring) process, is discharged onto a discharge tray 708.
However, since the spine, which projects from the grip portions 702 and 703, of the booklet 701 is pressed, the deformed portions 709a and 709b of the spine, which are subject to the deforming process, might protrude outward as illustrated in FIG. 21F, when the protruding amount is great. This gives less attractive appearance. Further, there arises a problem that, when the grip portions 702 and 703 hold the booklet 701, a pressing mark is formed at the portion around the spine of the booklet 701 by the corner portions 702a and 703a of the grip portions 702 and 703.
FIG. 22 illustrates the spine of the booklet that is subject to the squaring process. The corners 709a and 709b of the squared spine spread in the thickness direction of the booklet, so that the width of the squared plane unfavorably becomes greater than the thickness of the booklet. Further, the above-mentioned pressing mark is formed. Further, the sheet spine 709c at the center of the booklet, which does not have to be normally squared, is unfavorably deformed.